UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


Factors  Influencing  the  Development 

of  Internal  Browning  of  the  Yellow 

Newtown  Apple 

BY 

E.  L.  OVERHOLSER,  A.  J.WINKLER  AND  H.  E.  JACOB 


BULLETIN  No.  370 

September,  1923 


UNIVERSITY  OF  CALIFORNIA   PRESS 

BERKELEY,  CALIFORNIA 

1923 


FACTORS    INFLUENCING   THE    DEVELOPMENT   OF 

INTERNAL  BROWNING  OF  THE  YELLOW 

NEWTOWN  APPLE 

By  E.  L.  OVERHOLSER,  A.  J.  WINKLER  and  H.  E.  JACOB 


Previous  to  1905  it  had  been  noted  that  apples  grown  in  the  Pajaro 
Valle3r,  California,  were  affected  by  a  browning  of  the  flesh  of  the 
fruit  when  held  in  cold  storage.  The  browning  occurred  while  the 
tissue  was  firm  and  was  distinct  from  the  discoloration  which  accom- 
panies breakdown  of  the  tissues  in  storage  from  over-ripeness,  or  from 
freezing.  The  disease  is  known  as  " Internal  Browning"  and  is  most 
severe  with  the  Yellow  Newtown. 

The  earliest  reports  of  loss  from  this  trouble  date  from  the  crop  of 
1899.*  Powell14- 15  mentioned  the  browning  as  a  storage  problem. 
Stubenrauch17'  18  indicated  a  relation  between  internal  browning  and 
the  storage  temperature.  Several  reports  of  the  Bureau  of  Plant 
Industry f  mention  the  trouble  and  in  the  report  for  1920  it  is  stated 
that  no  relation  exists  between  the  acidity  of  the  fruit  and  the  brown- 
ing and  that  as  yet  no  definite  cause  can  be  attributed  to  the  disease. 

Recently  Ballard,  Magness  and  Hawkins2  and  Winkler19  have  pub- 
lished a  full  account  of  their  studies  of  internal  browning. 

OBJECTS  OF  THE  INVESTIGATIONS 

The  investigations  reported  herewith  were  undertaken  in  an 
attempt  to  determine  (1)  the  field  conditions  responsible  for  the  sus- 
ceptibility of  the  fruit  to  browning  and  (2)  the  factors  immediately 
responsible  for  its  development  in  storage. 

DESCRIPTION  OF  INTERNAL  BROWNING 

In  Yellow  Newtown  apples  stored  at  32°  F.,  the  browning  first 
becomes  noticeable  during  the  latter  part  of  December.  When  stored 
at  higher  temperatures  its  appearance  is  delayed.  At  temperatures 
above  50°  F.,  the  disease  usually  does  not  develop. 


*  Letter  from  W.  A.  Taylor,  Chief  of  the  Bureau  of  Plant  Industry,  U.  S.  D.  A. 
(1920). 

t  U.  S.  D.  A.  Bureau  of  Plant  Industry  Reports  1910-17-18  and  20. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  disease  is  non-parasitic  and  affects  the  large  isodiametric  cells 
of  the  pulp.  It  can  be  first  detected  in  cross  sections  of  the  apple  in 
somewhat  elongated  areas  radiating  outward  from  the  central  portion 
in  the  region  opposite  the  basal  end  of  the  carpels.  The  areas  first 
browned  lie  adjacent  to  and  radiate  outward  from  the  primary 
vascular  bundles. 

The  browning  spreads  most  rapidly  in  the  region  of  the  secondary 
vascular  bundles.  It  may  develop  well  toward  the  calyx  end,  along 
the  vascular  bundles  even  before  penetrating  appreciably  into  the 
pulp  laterally  near  the  point  of  initial  browning.  The  bundles  them- 
selves, however,  are  slow  to  brown.  The  large  cells  adjacent  to  the 
bundles  first  become  affected,  then  the  small  cells  and  finally  the 
bundles. 

In  the  more  advanced  stages,  the  browning  may  spread  throughout 
the  pulp  and  resemble  storage  breakdown.  When  the  development  of 
the  disease  reaches  an  advanced  stage,  the  small  thick-walled  cells  of 
the  epidermis  become  browned,  and  the  fruit  appears  scalded.  In  the 
earlier  stages,  however,  the  epidermis  appears  normal,  the  flesh 
remains  firm  and  the  disease  is  detected  only  by  cutting  into  the  fruit. 

METHODS  OF  PROCEDURE 

The  storage  phases  of  the  problem  were  conducted  in  the  Division 
of  Pomology  cold  storage  plant,  consisting  of  six  rooms  and  two  large 
insulated  boxes.  Temperatures  of  30°,  32°,  36°,  40°,  45°,  57°,  and 
70°  P.,  were  obtained  within  ±1°  F.,  with  the  exception  of  the  two 
higher  temperatures  which  varied  more  widely.  During  the  season  of 
1919  the  temperature  of  the  32°  P.  room  accidentally  dropped  suffi- 
ciently low  for  a  short  period  of  time  to  cause  slight  freezing  of  the 
earlier  picked  apples.  Such  fruit  was  discarded.  The  humidity  in 
each  of  the  different  rooms  was  fairly  constant  and  did  not  vary  more 
than  3  to  4  per  cent. 

The  fruit  was  obtained  from  the  Rodgers  Brothers  Orchards,* 
located  near  Watsonville  in  the  Pajaro  Valley.  The  apples  were 
packed,  labeled,  and  shipped  by  express  to  Berkeley  with  minimum 
delay.  The  fruit  with  few  exceptions  represented  tree-run  apples. 
The  time  of  harvest  closely  conformed  to  the  middle  of  the  commercial 
picking  season,  except  in  the  case  of  fruit  picked  to  determine  the 


*  The  writers  are  greatly  indebted  to  Messrs.  C.  J.  and  Marion  Rodgers  for 
their  interest  and  hearty  cooperation,  which  enabled  fruit  to  be  obtained  and 
certain  trees  to  be  kept  under  observation. 


x;/ 


- 


<\lmk 


ff 


Color  plate  showing  the  degrees  of  internal  browning  recorded. 
A.  Normal  apple.     B.   Trace  browning.     C.   Slight  browning.     D.  Bad  browning. 

E.  Very  bad  browning. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/factorsinfluenci370over 


BULLETIN  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  5 

effect  of  maturity  when  harvested.  For  this  purpose  the  earliest  pick- 
ing was  made  as  the  regular  picking  began,  the  second  about  the 
middle,  and  the  third  at  the  close  of  the  harvesting  season.  Each  lot 
represented  fruit  from  a  single  tree. 

Upon  receipt  at  the  storage  plant,  the  lots  were  divided  into  the 
necessary  number  of  sub-lots  for  the  particular  experiment.  The  sub- 
lots  of  from  80  to  100  specimens  each  were  stored  in  apple  boxes.  The 
boxes  were  placed  so  that  sufficient  space  was  maintained  for  normal 
ventilation  in  storage.  Apples  of  the  same  lot  were  used  in  each  experi- 
ment and  check,  and  as  nearly  identical  conditions  as  possible  were 
maintained  except  for  the  factor  being  tested. 

Since  internal  browning  affects  the  flesh  of  the  fruit  it  was  neces- 
sary to  cut  the  apples  in  order  to  make  the  observations.  Browning 
could  be  best  detected  by  cutting  perpendicular  to  the  axis  of  the 
core  in  a  plane  passing  through  the  junction  of  the  carpels  with  the 
stem. 

Four  observations  were  made  each  season  at  monthly  intervals, 
beginning  in  January.  Twenty  specimens  from  every  sub-lot  were  cut 
at  each  of  the  four  seasonal  observations.  By  cutting  several  hundred 
specimens  from  time  to  time  it  was  determined  that  the  error  in  cut- 
ting only  twenty  specimens  ranged  from  2  to  5  per  cent,  and  this 
error  was  reduced  when  the  four  seasonal  cuttings  were  averaged. 

Definition  of  terms. — The  terms  employed  in  recording  the  observa- 
tions to  designate  the  degree  of  browning  are  defined  as  follows : 

1.  Normal. — Apples  in  which  no  browning  was  apparent  to  the 
unaided  eye  (fig.  1.) 

2.  Trace  Browning. — When  browning  was  present  in  the  flesh  to 
a  recognizable  degree,  but  not  of  sufficient  severity  to  lessen  the  market 
value  (fig.  2). 

3.  Slight  Browning. — When  browning  was  sufficiently  severe  to 
lessen  the  market  quality,  but  not  to  such  a  degree  as  to  render  the 
apples  objectionable  for  culinary  purposes  (fig.  3). 

4.  Moderate  Browning. — When  the  fruit  was  rendered  unsuitable 
for  ordinary  culinary  purposes  (fig.  4). 

5.  Severe  Browning. — When  the  structure  of  the  tissue  exhibited 
a  marked  degree  of  disintegration,  and  gave  the  apples  an  appearance, 
upon  cutting,  of  being  rotten  within  (fig.  5). 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

I.  The  Relation  of  Orchard  Conditions  to  the  Development 
of  Internal  Browning  in  Storage 


The  Relative  Severity  of  Internal  Browning  of  Yellow 

Newtown  Apples  Grown  in  the  Pajaro 

Valley  and  Elsewhere 

In  order  to  determine  whether  the  browning  was  confined  solely 
to  apples  grown  in  the  Pajaro  Valley,  California,  apples  were  obtained 
from  other  localities  in  the  state  and  even  from  districts  in  other  states 
where  the  Yellow  Newtown  is  successfully  grown.  The  fruit  was 
shipped  by  express  to  Berkeley  and  stored  throughout  the  season  under 
similar  conditions  at  32°  F.    The  results  are  shown  in  table  1. 


TABLE   1 

The  Occurrence  and  Intensity  of  Internal  Browning  of  Yellow  Newtown 
Apples  Grown  in  Various  Districts 


Season 

Source  of  fruit 

Degree  of  brow 

ning 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight    . 

Per  cent 
moderate 

Per  cent 
severe 

1919 

Oakglen,    Cal.      Foothills    of 
southern  California 

80 

100 

97 

95 

50 

100 

95 

5 

20 
0 
3 

5 

42 

0 

5 

20 

0 
0 
0 

0 

8 

0 

0 

22 

0 
0 

0 
0 

0 

0 

0 

33 

0 

1919 

Mariposa  Mts.      Foothills  of 
Sierras 

0 

1919  and 
1920 
1919 

Ben  Lomond,  Cal.    Hills  bor- 
dering Pajaro  Valley 

Oregon    Agricultural    Experi- 
ment   Station,    Willamette 
Valley 

0 
0 

1919  and 
1920 

Cornell   Agricultural   Experi- 
ment Station,  Western  New 
York 

0 

1920 

Dutchess  Co.,  New  York,  Hud- 
son River  Vallev 

0 

1920 

Albemarle  Co.,  Virginia 

0 

1919  an  -1 

Pajaro  Valley,  California  .  . 

20 

1920 

These  figures  indicate  that  Yellow  Newtown  apples  are  generally 
susceptible  to  internal  browning.  The  disease  in  apples  from  other 
regions  than  the  Pajaro  Valley,  however,  has  not  been  sufficiently 
severe  to  render  it  an  economic  problem. 


Bulletin  870 


BROWNING    OF    YELLOW    NEWTOWN    APPLES 


The  fact  that  the  apples  from  nearly  all  sections  showed  browning 
indicates  there  is  either  something  peculiar  to  the  variety  which 
makes  it  susceptible  to  browning,  or  that  the  trouble  lies  in  the  regions 
in  which  it  is  at  present  most  extensively  grown.  Both  of  these  con- 
ditions appear  to  be  more  or  less  responsible  for  the  browning.  The 
fact  that  other  varieties  of  apples  grown  in  the  same  districts,  with 
the  exception  of  the  Pajaro  Valley,  are  immune  to  this  disease  would, 
at  least,  suggest  that  the  Yellow  Newtown  exhibits  a  varietal  char- 
acteristic of  susceptibility  to  internal  browning. 

The  effect  of  the  region  in  which  the  fruit  is  grown  upon  its  sus- 
ceptibility to  browning  is  indicated  by  the  fact  that  several  additional 
varieties  of  apples,  as  the  Yellow  Bellflower  and  the  Red  Pearmain, 
which  show  no  tendency  to  browning  in  other  sections,  become  suscept- 
ible to  this  disease  when  grown  in  the  Pajaro  Valley.  Furthermore,  the 
Yellow  Newtown,  when  grown  in  this  valley  is  more  susceptible  to 
internal  browning  than  when  grown  elsewhere.  Mackie,11  as  a  result 
of  a  soil  survey  of  the  Pajaro  Valley,  is  of  the  opinion  that  the  sus- 
ceptibility to  the  disease  is  not  due  to  soil  conditions.  The  climatic 
conditions  of  the  Pajaro  Valley,  therefore,  apparently  exert  an  influ- 
ence upon  the  development  of  apples  which  have  not  been  shown  to 
similarly  occur  elsewhere,  and  which  render  them  susceptible  to  this 
disease. 

The  Relation  of  the  Age  of  the  Tree  to  Internal  Browning 

The  belief  has  been  expressed  by  growers  and  by  cold  storage  men, 
that  fruit  from  young,  vigorous  trees,  just  coming  into  bearing,  is 
more  subject  to  internal  browning  than  fruit  of  vigorous  trees,  well 
advanced  into  the  productive  period.  To  test  this  opinion,  a  storage 
experiment  was  started  in  1918  to  determine  the  relation  of  the  age  of 
the  trees  to  the  browning  of  the  fruit.  For  each  of  the  five  storage 
seasons  during  which  observations  were  made  upon  this  phase  of  the 
problem,  the  same  trees  were  compared.  The  old  but  vigorous  trees 
were  in  the  prime  of  their  productiveness,  while  the  young  vigorous 
tree'4  were  just  coming  into  bearing  at  the  time  this  work  was  started. 
Table  2  represents  four  seasons'  average  of  the  per  cent  of  internal 
browning  for  all  the  lots  of  the  old  and  the  young  trees,  respectively. 

These  data  indicate  a  slight  relation  between  age  of  trees  and 
internal  browning.  The  authors  believe,  however,  that  differences  in 
the  maturity  of  the  fruit  from  the  old  and  the  young  trees  when 
picked,  may  affect  the  degree  of  browning  to  a  certain  extent.  The 
fruit  collected  from  the  old  trees  was,  as  a  rule,  earlier  in  ripening 


8 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


than  that  from  the  young  trees.  The  maturity  of  the  fruit  when 
harvested  is  shown  later  to  affect  the  relative  degree  of  browning. 
Furthermore,  the  vigor  of  vegetative  growth  as  affected  by  age  of  tree 
would  also  influence  the  degree  of  browning. 

TABLE  2 

The  Effect  of  Age  of  Tree  Upon  Browning  of  Apples 


Seasons 
averaged 

Number 

of  boxes 

tested 

Average  degree  of  browning 

Age  of  trees 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Old 

1918  to 
1922,  inc. 
1918  to 
1922,  inc. 

25 
25 

25 
33 

32 
31 

18 
10 

15 
14 

Young 

10 

12 

The  Relation  of  Size  of  Crop  Borne  by  the  Tree  to  Internal 

Browning 
During  the  seasons  of  1918  to  1921,  inclusive,  fruit  was  harvested 
from  trees  bearing  a  full  crop  and  from  trees  bearing  a  light  crop  to 
determine  the  effect  of  the  size  of  crop  being  matured  by  a  tree  upon 
the  susceptibility  of  its  fruit  to  browning.  The  fruit  was  stored  at 
32°  F.  and  the  average  per  cent  of  normal  and  brown  fruit  for  the 
three  years  is  given  in  table  3. 

TABLE  3 
The  Relation  of  Size  of  Crop  Borne  by  the  Tree  to  Internal  Browning 


Extent  of  crop 
per  tree 

Number  of  boxes 
tested 

Per  cent  normal 
fruit 

Per  cent 
browned  fruit 

Light 

27 
18 

15 
70 

85 

Heavy 

30 

The  data  indicate  that  the  fruit  from  trees  bearing  a  heavy  crop 
is  less  susceptible  to  browning  in  storage  than  fruit  from  trees  bearing 
a  light  crop. 

This  is  substantiated  by  the  fact  that  tree  No.  9  had  a  medium  crop 
in  1918-19  and  the  fruit  showed  40  per  cent  browning,  but  in  1919-20 
and  1920-21  the  crops  borne  were  very  heavy  and  during  those  years 
no  browning  occurred.  Tree  No.  10  had  a  moderately  heavy  crop  in 
1918-19  and  during  the  two  following  seasons  produced  crops  suc- 
cessively lighter.  The  percentages  of  fruit  showing  browning  during 
those  years  were  35,  50  and  55,  respectively. 


Bulletin  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES 


The  Relation  of  the  Vigor  of  the  Tree  to  Internal  Browning 

Tests  concerning-  the  relation  of  tree  vigor  to  internal  browning 
were  begun  during  the  season  of  1917-18.  Five  years'  data  are  avail- 
able in  comparing  very  vigorous  with  weak  trees,  and  this  is  con- 
trasted with  four  years'  data  obtained  from  moderately  vigorous 
trees.  The  fruit  was  stored  at  both  32°  F.  and  36°  F.,  but  the  data 
presented  in  table  4,  represent  the  averages  of  both  temperatures  for 
all  years. 

TABLE  4 
Relation  of  Tree  Vigor  to  Internal  Browning 


Vigor  of  trees 

Number 

of 
seasons 
averaged 

Number 

of 

boxes 

tested 

Average  degree  of  browning 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Very  vigorous 

5 
4 
5 

30 
25 
30 

25 

64 
20 

43 
24 
36 

11 

5 

18 

11 

3 
15 

10 

Moderately  vigorous 

Weak 

4 
11 

These  data  show  that  apples  from  trees  of  very  low  vegetative  vigor 
brown  considerably  more  than  those  from  trees  of  moderate  or  normal 
vigor.  Furthermore,  apples  from  trees  of  unusually  high  vigor  pro- 
duce fruit  less  resistant  to  browning  than  that  produced  by  trees  of 
normal  vigor. 

During  the  season  of  1921  fruit  was  harvested  at  the  three  different 
stages  of  maturity  from  a  tree  having  several  branches  which  were 
suffering  from  sunscald  and  disease,  making  practically  no  new  ter- 
minal growth,  and  which  possessed  scanty  foliage,  deficient  in  chloro- 
phyll. Other  portions  of  the  same  tree  had  vigorous  growing  branches 
possessing  abundant  dark  green  foliage  from  which  fruit  was  also 
harvested.  The  fruit  was  stored  at  32°  F.  for  five  months,  and  the 
results  which  substantiate  those  previously  presented  are  given  in 
table  5. 

TABLE  5 

The  Kelative  Browning  of  Fruit  from  Weak  and  Vigorous  Branches 
Upon  the  Same  Tree  (1921) 


Number 

of 

boxes 

Average  degree  of  browning 

Vigor  of  branches 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Vigorous 

3 
3 

38 
29 

21 

28 

20 

27 

19 
16 

1 

Weak 

0 

10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  Relation  of  Maturity  of  Fruit  When  Harvested  to 
Internal  Browning 

Powell  and  Fulton,14  Brooks,  Cooley  and  Fisher,4'  5*  6  and  others 
have  emphasized  the  importance  of  the  maturity  of  the  fruit  when 
harvested,  in  the  control  of  certain  non-parasitic  diseases  of  the  apple. 
Cold  storage  managers  have  believed  that  the  occurrence  of  internal 
browning"  was  partially  due  to  an  immature  condition  of  the  apples 
when  stored ;  and  apples  permitted  to  remain  on  the  trees  until  they 
had  a  higher  sugar  content,  according,  to  these  men,  were  more 
resistant  to  browning. 

An  investigation  of  the  relation  of  the  maturity  of  the  fruit  to 
internal  browning  was  conducted  during  the  seasons  of  1919  to  1921, 
inclusive.  Three  pickings  of  fruit  were  made  each  season.  The  fruit 
of  the  first  picking  was  ' '  hard  green ' '  in  maturity  and  of  a  solid  green 
color;  that  of  the  second  picking  was  "firm  green"  and  signs  of  the 
yellow  color  were  becoming  evident ;  while  the  fruit  of  the  last  picking 
was  somewhat  "over-ripe"  for  harvesting  and  showed  considerable 
yellow  color  over  the  entire  surface.  The  fruit  for  each  lot  was  taken 
from  the  same  trees  at  each  of  the  pickings.  Uniformity  of  the  lots 
was  obtained  by  taking  fruit  from  all  portions  of  the  tree  at  each 
picking.  The  apples  of  each  tree  for  the  several  pickings  were  stored 
under  identical  conditions  at  32°  F.  and  36°  F.  The  average  results 
of  three  season's  observations  are  given  in  table  6. 

TABLE   6 
Eelation  of  Maturity  of  Fruit  to  Internal  Browning 


Number 
boxes 

testes 

Average  degree  of  browning 

Period  of  harvest 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Early 

36 

27 
27 

42 
31 
15 

31 

38 
35 

12 
15 
25 

10 
14 

18 

5 

Medium 

5 

Late 

7 

These  figures  show  a  definite  relation  of  maturity  of  the  fruit  at 
time  of  harvest  to  susceptibility  to  internal  browning,  the  more  mature 
fruit  browning  more  severely  in  every  test.  The  mature  fruit  not  only 
browned  more  severely,  but  developed  the  disease  more  rapidly.  This 
fact  is  shown  in  table  7,  which  represents  the  averages  for  all  the  lots 
of  each  picking  for  the  season  of  1920-21. 


Bulletin  370]      BROWNING    OF    YELLOW   NEWTOWN    APPLES 


11 


TABLE  7 
The  Kelation  of  Maturity  of  the  Fruit  to  the  Bate  of  Development 

of  Browning 


Temperature 
of  storage 

Date  of 
picking 

Date  of 
storage 

Time  in 

storage 

Per  cent  of  marketable* 
and  unmarketable  fruit 

marketable 

Unmarketable 

32°F. 
32°F. 
32°F. 

Nov.    6 
Oct.    16 
Sept.  26 

Nov.  16 
Oct.    19 
Sept.  26 

6  weeks 
15  weeks 
20  weeks 

61 
62 
60 

39 
38 
40 

♦Marketable  fruit  included  both  "normal"  and  the  "trace  browned"  specimens;  unmarketable 
included  "slight,"  "moderate"  and  "severely  browned"  specimens. 

The  apples  picked  latest,  browned  approximately  two  and  one-half 
times  as  rapidly  as  those  picked  in  the  middle  of  the  normal  harvest 
period.  Fruit  picked  in  the  middle  of  the  season  browned  about  one 
and  one-third  times  as  rapidly  as  that  picked  at  the  beginning  of  the 
harvest  period. 

The  total  sugar  content  as  determined  by  chemical  analysis  at  the 
time  of  harvest  of  the  fruit  picked  September  26,  October  16,  and 
November  6,  was  9.4,  10.0  and  11.4  per  cent,  respectively.  This  shows 
that  a  higher  sugar  content  does  not  inhibit  browning.  In  fact 
Winkler19  found  by  analysing  a  large  number  of  samples,  that  the 
sugar  content  did  not  influence  the  resistance  or  susceptibility  of  the 
fruit  to  the  disease. 

Ballard,  ct  al.,2  in  their  summary  state  that  apples  high  in  sugar 
and  acid  content  tended  to  become  browned  to  a  much  greater  extent 
than  normal  fruit.  Winkler19  found  that  decrease  in  total  acidity  did 
not  influence  the  resistance  of  the  fruit  to  browning.  He  determined 
that  although  the  titrable  acidity  decreased  with  maturity  and  subse- 
quent storage,  the  active  acidity,  as  indicated  by  the  pH  value  of  the 
expressed  juice,  remained  practically  constant. 


The  Effect  of  Orchard  Temperature  Upon  Internal  Browning 

Many  of  the  leading  fruit  men  of  the  Pajaro  Valley  attribute  the 
occurrence  of  internal  browning  to  the  cold  foggy  weather  which 
usually  prevails  during  the  latter  part  of  July  and  August,  at  the 
time  the  fruit  is  growing  most  rapidly. 

With  these  observations  as  a  basis,  experiments  were  started  in 
the  spring  of  1920  to  determine  the  effect  of  orchard  temperature  and 
fog  upon  internal  browning.  During  the  first  week  of  May,  1920,  a 
tent  was  erected  over  a  single  average  tree  which  bore  a  normal  set  of 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

fruit.  A  framework  was  built  over  the  tree  and  covered  with  black 
cambric  cloth  to  within  about  six  feet  of  the  ground.  Thus,  all  the 
branches  with  fruit  were  shaded  continuously.  At  the  top  on  the  north 
side,  a  six-inch  strip  extending  the  entire  length  of  the  tent  was  left 
open,  which  permitted  a  good  ventilation  of  the  tent.  Otherwise,  this 
tree  was  given  the  identical  treatment  as  the  remainder  of  the  orchard. 
At  the  same  time  the  tent  was  erected,  100  individual  apples  on  an 
adjacent  tree  were  placed  in  black  cloth  bags.  A  similar  number  of 
apples  on  adjoining  trees  were  placed  in  black  bags  on  the  first  of  June 
and  July,  respectively. 

During  the  season  of  1921  the  experiment  was  repeated,  except 
that  two  tents  were  constructed  over  separate  trees  and  in  one  of  the 
tents  two  oil  stoves,  with  accessory  oil  tanks  were  kept  burning  con- 
tinuously throughout  the  season  until  two  pickings  had  been  obtained 
in  the  fall,  when  the  tent  was  accidentally  destroyed  by  fire.  Further- 
more, apples  were  enclosed  in  white  as  well  as  in  black  bags.  One 
hundred  specimens  each  were  placed  in  both  the  white  and  black  bags 
upon  the  following  dates :   May  10,  June  10,  July  15,  and  August  26. 

Owing  to  the  lack  of  necessary  equipment,  it  was  impossible  to 
measure  the  exact  effect  of  the  tent  and  black  bags  upon  the  light 
intensity.  Nevertheless,  it  is  thought  that  the  light  exclusion,  as  such, 
was  negligible,  since  it  had  little  or  no  effect  upon  the  amount  of 
browning  as  shown  by  table  8. 

This  indication  as  to  the  unimportance  of  the  decreased  light  inten- 
sity of  the  valley  because  of  fogs,  is  confirmed  by  the  graphs  in  chart 
1,*  which  represent  the  total  number  of  cloudy  and  partly  cloudy  days 
for  the  Pajaro  Valley,  California;  Albermarle  County,  Virginia;  and 
the  Rogue  River  Valley,  Oregon.  These  localities  are  among  the  most 
important  regions  in  the  production  of  the  Yellow  Newtown  apple. 
The  graphs  show  that  in  Virginia  where  the  apples  do  not  brown,  there 
are  approximately  the  same  number  of  cloudy  and  partly  cloudy  days 
for  the  months  concerned  as  there  are  in  the  Pajaro  Valley  where 
browning  is  a  serious  problem.  In  the  Rogue  River  Valley,  where 
browning  also  is  not  a  problem,  there  are  a  few  cloudy  days.  It  is 
questionable,  however,  as  to  whether  or  not  this  factor  has  any  appre- 
ciable direct  effect  upon  the  resistance  of  the  apple  to  this  disease  as 
will  be  brought  out  later  in  the  relation  of  temperature  to  browning. 
The  number  of  cloudy  or  partly  cloudy  days  would  exert  an  indirect 
effect  by  influencing  the  temperature  of  the  atmosphere  and  to  a 
greater  degree  of  the  fruit  (table  8). 


*  Records  fiom  Climatological  Data  Reports.     U.  S.  Dept.  of  Agr.  Weather 
Bureau,  1905  to  1920. 


BULLETIN  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES 


13 


The  effect  of  the  tent  and  black  bags  upon  the  temperature  was 
very  striking.  The  daily  mean  temperature  at  the  core  of  the  fruit 
in  black  bags  as  indicated  by  self -recording  thermometers,  was  nearly 
10°  F.  higher  than  that  of  apples  normally  exposed.  In  case  of  the 
tented  tree,  a  lower  mean  temperature  was  maintained  by  the  shading 
and  lack  of  circulation  of  the  air.  Here  the  temperature,  as  recorded 
by  accurately  regulated  thermographic  instruments,  was  found  to  be 
about  5°  F.  lower  than  the  air  temperature. 


110 

100 

CHART 

1 

. 

1 

*L 

^^^ 

90 
80 
70 
60 

*-. 

1 

/ 
\    / 

s       1 T 

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40 
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20 
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i 

\ 

\ 

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\^-~- 

1905*06   *07«03    '09    'lO'll  -  Years  -    »15    »16 '»17*18    '19  1920 

Chart  1. — The  total  number  of  cloudy  and  partly  cloudy  days  for  June,  July, 
August,  and  September  for  a,  Pajaro  Valley,  California;  b,  Albermarle  County, 
Virginia,  and  c,  Rogue  River  Valley,  Oregon. 


The  fruit  outside  the  tents  had  an  average  higher  temperature  than 
the  air  temperature,  as  a  result  of  heat  absorption  during  periods  of 
sunshine.  The  fruit  under  the  tents  had  a  temperature  practically 
identical  with  the  air  temperature  of  the  tent.  These  temperature 
differences  emphasize  the  effect  of  sunshiny  days  as  contrasted  with 
foggy  or  cloudy  days.  On  foggy  days  the  fruit  not  tented,  regardless 
of  the  treatment  given,  approached  the  temperature  of  the  open  air. 
When  the  sun  was  shining,  however,  the  temperature  of  exposed  fruits 
averaged  nearly  ten  degrees  higher  than  air  temperature. 


14 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


be 
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temper- 
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foggy 
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ature 
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CO    iO 

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Average 
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78.9  F 
71. 7F* 
69. 5F* 
71.6  F 

a 

CD 

1 

83 

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H 

ii 

Normally  ex- 
posed apples. . 

Heated  tent 

Unheated  tent  . 
Air  temperature 

i-H  ^ 


BULLETIN  370]      BROWNING    OF   YELLOW   NEWTOWN    APPLES 


15 


The  bagged  fruit  and  checks  from  similar  positions  on  the  same 
trees  were  harvested  at  the  first  two  pickings.  The  fruit  from  the 
tented  tree,  with  fruit  from  two  adjacent  trees  for  checks,  was  also 
harvested  at  these  first  pickings.  All  of  the  lots  and  checks  were  stored 
under  identical  conditions  at  32°  F.  The  results  of  these  experiments 
are  given  in  table  8.  As  all  the  bagged  fruit  behaved  similarly,  only 
the  average  for  all  the  lots  is  given.  The  same  is  true  for  the  fruit  of 
the  tented  tree  and  the  checks. 

CHAET  2 


76 

74 

— ■  ,* 

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/ 
/ 

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54. 

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1 

1905*06  »07'08   ^'lO  fll  -  Years  -   »15   *W\1  'lS']^  1920 

Chart  2. — The  average  temperature  for  June,  July,  August,  and  September 
for  a,  Albermarle  County,  Virginia;  b,  Rogue  River  Valley,  Oregon,  and  c, 
Pajaro  Valley,  California. 


These  data  indicate  a  definite  relationship  between  the  orchard 
temperature  and  internal  browning.  A  daily  mean  temperature  of 
about  9°  F.  above  the  temperature  of  the  normally  exposed  fruit  in 
the  orchard  reduced  the  browning  to  a  marked  degree.  Conditions 
which  resulted  in  the  fruit  temperatures  being  below  that  of  normally 
exposed  fruit  materially  increased  the  amount  of  browning. 

This  relation  between  orchard  temperature  and  the  amount  of 
browning  becomes  more  impressive  when  the  temperature  records  of 
this  valley  are  compared  with  the  years  of  severe  and  of  moderate  or 
no  browning  for  this  region,  and  with  the  temperature  records  of  other 


16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


districts  where  this  variety  of  apple  grows  satisfactorily,  but  where  the 
browning  is  not  a  problem.  The  graphs  in  chart  2*  represent  the 
mean  temperature  for  June,  July,  August  and  September  for  the 
Pajaro  Valley,  California;  Albemarle  County,  Virginia;  and  Eogue 
River  Valley,  Oregon.  If  the  record  for  the  Pajaro  Valley  is  observed, 
it  will  be  seen  that  in  1908  and  in  1914,  years  in  which  very  heavy 
losses  through  internal  browning  occurred,  the  mean  temperature  for 
these  four  months  was  very  low.  For  1915  and  1916,  respectively, 
when  the  mean  temperature  for  these  growing  months  was  nearer  the 
normal  value,  the  severity  of  the  browning  was  also  less.  In  1912, 
1913,  1917  and  1918,  years  of  higher  mean  temperature  for  the  months 
of  rapid  growth,  however,  there  was  little  or  no  browning  in  the  com- 
mercial storage  plant.  Comparing  the  temperature  records  of  the 
Pajaro  Valley  with  those  of  Rogue  River  Valley,  Oregon  and  Albe- 
marle County,  Virginia,  it  is  found  that  these  regions  have  a  mean 
temperature  of  5°  F.  and  11.6°  F.  higher,  respectively,  than  that  of 
the  Pajaro  Valley. 

The  Effect  of  Exposure   (Position  of  the  Fruit  on  the  Tree) 
Upon  Internal  Browning 

Results  which  further  confirm  this  relation  of  orchard  temperature 
to  browning  were  obtained  by  collecting  fruit  from  well  exposed  and 
shaded  portions  of  the  tree.  During  the  seasons  of  1920  and  1921, 
fruit  was  collected  from  the  upper  southwest  periphery  of  two  trees, 
where  the  fruit  received  the  maximum  effect  of  the  sun's  rays,  and 
also  from  the  lower  north  part  of  the  same  trees  where  the  fruit  was 
continuously  in  the  shade.  The  lots  were  stored  under  identical 
conditions  at  32°  F.    The  results  are  given  in  table  9. 

TABLE  9 

The  Effect  of  Exposure  Upon  Internal  Browning 


Position  of  fruit 

Average 
fruit 
tempera- 
ture 
during  day 

Number  of 
seasons 
averaged 

Average  degree  of  browning 

on  tree 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Well  exposed  on  S. 
W.  periphery  of 
tree 

81°F. 
67°F. 

2 

2 

42 

22 

44 
43 

11 

22 

3 
12 

0 

Shaded  interior  N. 
side  of  tree 

1 

*  Becords  from  Climatological  Data  Reports.     U.  S.  Dept.  of  Agr.  Bureau, 
1905  to  1920. 


BULLETIN  370]      BROWNING   OP   YELLOW   NEWTOWN   APPLES 


17 


These  figures  show  nearly  twice  as  much  browning  in  fruit  from 
the  same  trees  when  picked  from  the  shaded  portions  as  contrasted 
with  the  exposed  portions.  Temperature  records  show  that  during  the 
dajr  the  temperature  of  the  well  exposed  fruit  averaged  about  14°  F. 
higher  than  that  from  the  shaded  side  of  the  tree. 


The  Relation  op  Self-  vs.  Cross-Pollination  to  Internal 
Browning   (1919-20) 

In  the  spring  of  1919,  in  connection  with  the  pollination  experi- 
ments, a  single  Yellow  Newtown  tree  was  enclosed  in  an  insect-proof 
mosquito-bar  tent,  in  which  was  placed  a  hive  of  bees.  As  a  result,  all 
the  fruit  that  set  was  from  self-pollination.  A  Yellow  Newtown  and 
a  Yellow  Bellflower  tree  were  also  enclosed,  together,  within  a  single 
tent  containing  a  hive  of  bees.  A  very  heavy  set  of  Yellow  Newtown 
resulted  and  it  was  assumed  that  a  large  percentage  of  these  were 
cross-pollinated  fruits.  In  addition  the  Yellow  Newtown  was  selfed 
and  crossed  with  Yellow  Bellflower  by  hand.  The  data  are  presented 
in  table  10. 


TABLE  10 

Relation  of  Self-  vs.  Cross-Pollination  to  Internal  Browning  (1919-20) 


Number 
specimens 

Average  degree  of  browning 

Pollination 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Yellow  Newtown — Selfed 

225 
220 

28 
15 

54 
25 

14 

27 

4 
24 

0 

Yellow    Newtown    x    Yellow 
Bellflower 

9 

The  results  are  not  sufficiently  conclusive  to  state  that  cross-pollin- 
ation increases  the  susceptibility  of  the  Yellow  Newtown  to  internal 
browning,  but  they  strongly  indicate  at  least  that  provision  for  cross- 
pollination  cannot  be  expected  to  decrease  the  susceptibility  of  this 
variety  to  internal  browning. 


18 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


II.    The  Relation  of  Storage  Conditions  to  the  Development  of 
Internal  Browning 

The  Effects  of  Delayed  Storage  Upon  Internal  Browning 

The  Yellow  Newtown  apple  of  the  Pajaro  Valley  tends  to  drop 
prematurely;  hence  the  fruit  is  harvested  in  a  more  immature  state 
than  is  the  practice  with  this  variety  elsewhere.  Experiments  designed 
to  test  the  effect  of  delayed  storage  were  conducted  during  the  seasons 
of  1919  and  1920  by  permitting  the  fruit  to  ripen  at  room  temperature 
for  one  month  before  storing  at  32°  F.  The  fruit  was  kept  in  open 
boxes  throughout  the  experiments.     The  results  of  the  tests  are  given 

in  table  11. 

TABLE  11 

The  Effect  of  Delayed  Storage  Upon  Internal  Browning 


Number  of 
boxes 

Average  degree  of  browning 

Treatment 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Storage  delayed  four  weeks 

No  delay  in  storage 

9 
9 

16 
37 

36 

37 

27 
12 

12 
8 

9 
6 

The  amount  of  internal  browning  was  greatly  increased  by  the 
delayed  storage  in  all  of  the  tests.  This  increase  is  possibly  due  to  the 
fact  that  delayed  storage  resulted  in  the  fruit  being  more  mature  when 
placed  in  cold  storage.  Experiments  with  maturity  of  fruit  show  con- 
clusively that  the  more  mature  the  fruit,  the  more  susceptible  it  is 
to  internal  browning.  The  data  emphasize  the  necessity  of  quickly 
placing  the  fruit  in  storage  at  the  proper  temperature. 


The  Effect  of  Intermittent  Storage  Upon  Internal  Browning 

Experiments  were  conducted  to  determine  the  effect  of  intermittent 
storage  upon  internal  browning.  Apples  of  the  first  and  second  pick- 
ings from  the  same  trees  were  employed  during  the  seasons  of  1919 
and  1920.  One  portion  of  each  lot  was  left  continuously  in  storage  at 
a  temperature  of  32°  F. ;  another  portion  was  removed  to  room  tem- 
perature for  24  hours  every  two  weeks;  and  a  third  portion  was 
removed  to  room  temperature  for  48  hours  once  each  month.  There 
was,  however,  no  appreciable  difference  between  the  two  types  of  inter- 
mittent storage,  hence,  they  are  averaged  together  in  the  data  presented 
in  table  12. 


Bulletin  370]      BROWNING    OF    YELLOW    NEWTOWN    APPLES 


19 


TABLE  12 

The  Effect  of  Intermittent  Storage  Upon  Internal  Browning 


Number  of 
boxes 

Average  degree  of  browning 

Treatment 

Per  cent 
normal 

Per  cent 
trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

Intermittent  storage 

Continuous  storage 

5 
5 

15 
21 

36 
32 

26 
21 

14 
16 

8 
10 

These  data  show  no  promise  of  controlling  internal  browning  by  the 
practice  of  intermittent  storage,  and  emphasize  the  advisability  of 
keeping  the  fruit  continuously  in  storage  until  placed  upon  the  market. 


The  Effect  of  Storage  Temperature  Upon  Internal  Browning 

Investigations  by  Powell  and  Fulton14  indicated  that  all  apples 
could  be  best  stored  at  about  32°  F.  Losses,  however,  were  incurred 
through  the  browning  of  Pajaro  Valley  grown  Yellow  Newtown  apples 
when  stored  at  this  temperature.  Through  the  work  of  Stubenrauch17 
Pajaro  Valley  apples  have  been  stored  at  36°  F.  since  about  1910. 
Ballard,  et  al.,2  state  that  browning  can  be  largely  prevented  by  storing 
Pajaro  Valley  apples  at  36°  F.  to  38°  F. 

In  the  experiments  of  the  authors,  apples  from  the  Pajaro  Valley 
were  stored  at  32°  F.  and  36°  F.  for  five  seasons  and  it  was  found 
that  considerable  browning  occurred  after  February  1,  even  in  the 
fruit  stored  at  36°  F.  Aside  from  the  browning,  however,  the  apples 
stored  at  36°  F.  kept  satisfactorily  each  year.  Apples  were,  therefore, 
stored  at  various  degrees  of  temperature  above  36°  F.,  with  the  follow- 
ing objects :  (1)  To  determine  the  lowest  temperature  at  which  internal 
browning  will  not  develop  during  the  normal  storage  period.  (2)  To 
determine  whether  or  not  the  temperature  which  is  sufficiently  high  to 
prevent  internal  browning  is  also  sufficiently  low  for  practical  storage 
purposes. 

The  averages,  after  five  months  storage  each  season,  for  all  the  lots 
at  each  of  the  temperatures  for  the  season  during  which  the  respective 
temperatures  were  available,  are  recorded  in  table  13. 


20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


TABLE  13 

The  Effect  of  Storage  Temperature  Upon  Internal  Browning 


Storage 

Number 
seasons 
average 

Number 
boxes 
tested 

Degree  of  brown 

ing 

temper- 
ature 

Per  cent 
normal 

Per  cent 

trace 

Per  cent 

slight 

Per  cent 
moderate 

Per  cent 
severe 

30°F. 

2 

6 

10 

26 

24 

25 

15 

32°F. 

5 

15 

15 

25 

21 

25 

14 

36°F. 

5 

15 

35 

37 

16 

9 

3 

40°F. 

2 

6 

74 

23 

3 

0 

0 

45°F. 

3 

9 

95 

5 

0 

0 

0 

57°F. 

1 

3 

100 

0 

0 

0 

0 

70°F. 

2 

6 

100 

0 

0 

0 

0 

The  results  obtained  show  a  definite  relation  between  the  amount 
of  internal  browning  and  the  storage  temperature.  The  effect  of  a 
few  degrees  is  striking.  Browning  did  not  occur  in  any  of  the  fruit 
stored  at  a  temperature  of  57°  F.  or  above. 

Practically  no  browning  occurred  at  45°  F.  and  the  fruit  remained 
marketable  when  stored  at  40°  F.  in  that,  as  used  by  the  writers,  the 
term  "trace  browning"  was  not  considered  sufficient  to  lessen  the 
marketability  of  the  fruit. 

Apparently  internal  browning  does  not  occur  at  a  temperature 
which  is  but  few  degrees  above  those  used  in  the  commercial  storage 
of  apples.  The  question  naturally  arises  as  to  whether  or  not  apples 
can  be  stored  successfully  at  this  slightly  higher  temperature.  The 
Yellow  Newtown  is  one  of  the  best  keeping  apples,  It  is  commonly 
stored  in  basements  and  similar  facilities  of  the  home.  The  writers 
have  observed  apples  which  were  held  in  basement  storage  until  the 
middle  of  April  without  loss.  In  the  case  of  the  fruit  stored  in  the 
laboratory  (room  temperature)  during  1919-20  and  1920-21,  no  loss 
through  rot  occurred  until  after  March  1.  This  fruit  kept  well  despite 
the  fact  that  the  temperature  in  the  laboratory  fluctuated  considerably 
and  at  times,  when  the  room  was  closed,  became  rather  high.  In  the 
storage  plant,  all  the  fruit  kept  in  good  condition  throughout  the 
normal  storage  period,  which  ends  about  the  middle  of  April  for  this 
variety.  One  shipment  of  fruit,  however,  was  in  a  train  wreck  and 
developed  considerable  rot  at  all  the  temperatures,  the  amount  of  rot 
being  greatly  increased  by  only  a  few  degrees  rise  in  temperature. 


BULLETIN  370]      BROWNING    OF   YELLOW   NEWTOWN   APPLES 


21 


Thus  it  would  appear,  that  where  sound  fruit  is  used  and  prompt 
storage  under  uniform  conditions  is  possible,  the  fruit  can  safely  be 
held  at  temperatures  sufficiently  high  to  prevent  browning  without 
other  forms  of  deterioration  developing.  In  commercial  practice, 
however,  it  would  probably  not  be  expedient  to  store  apples  for  any 
prolonged  period  of  time  above  40°  F.  It  should,  nevertheless,  be 
advisable  to  store  the  apples  at  or  just  below  this  temperature,  since 
the  browning  developed  at  40°  F.  was  very  mild,  rarely  exceeding 
the  condition  classed  as  ' '  trace  browning. ' '  Thus  it  would  seem  pos- 
sible to  keep  this  variety  of  apple  satisfactorily  throughout  its  normal 
storage  season  by  storing  at  a  temperature  sufficient  to  retard  the 
development  of  the  usual  forms  of  deterioration  and  prevent  any 
browning  that  would  interfere  with  its  saleability. 

The  browning  was  not  only  increased  in  severity  as  the  temperature 
decreased  below  40°  F,,  as  shown  by  the  figures  in  table  13,  but  its 
development  was  also  more  rapid.  This  correlation  of  temperature  of 
storage  with  the  time  of  initial  appearance  and  the  subsequent  develop- 
ment of  the  browning  is  illustrated  by  the  graphs  in  chart  3.  The 
apples  stored  at  32°  F.  showed  browning  a  month  prior  to  its  detection 
in  the  fruit  stored  at  36°  F.,  and  the  apples  held  at  40°  F.  remained 
normal  for  almost  two  months  after  those  stored  at  36°  F.  had  begun 
to  brown. 


CHART  3 


'100 


90 


I  60  - 


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2.Z 

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1 

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6  a 

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^sT~ 

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\ 

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\ 

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r* 

■^ 

^ 

«fo.i 

\ 

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t 

" 

V 

t 

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£* 

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-J_ 

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5 

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14 

0 

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50 

160 

Chart  3. — The  effect  of  temperature  on  the  rate  of  development  of  internal 
browning. 


22 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  Effect  of  Carbon  Dioxide  and  Oxygen  Upon  the  Development 
of  Internal  Browning 

Carbon  Dioxide. — One  of  the  most  common  opinions  with  regard 
to  internal  browning  is  that  its  development  results  from  the  accumu- 
lation of  carbon  dioxide  in  the  storage  room.  To  determine  the  validity 
of  this  opinion,  apples  were  placed  in  approximately  90  per  cent 
carbon  dioxide  for  varying  intervals  of  time.  All  the  lots  were  then 
stored  in  ordinary  apple  boxes  at  32°  F.  until  the  final  observations 
were  made.    The  results  of  these  tests  are  given  in  table  14. 

TABLE  14 

The  Effect  of  Carbon  Dioxide  Upon  the  Development  of  Internal  Browning 


Degree  of  browning 

Treatment  and  time  stored 

Per  Cent 
normal 

Per  cent 
Trace 

Per  cent 
slight 

Per  cent 
moderate 

Per  cent 
severe 

1 .  Check — no  treatment  stored  8  weeks 

2.  In  carbon  dioxide  for  8  days;  stored  8 

weeks 

50 

90 
20 
50 

70 

50 

10 
70 
50 

30 

0 

0 

10 

0 

0 

0 

0 
0 
0 

0 

0 
0 

3.    Same  as  (1),  but  stored  12  weeks 

0 

4.     In  carbon  dioxide  for  12  weeks 

0 

5.     In  carbon  dioxide  for  14  days;  stored 
12  weeks 

0 

These  results  show  that  the  accumulation  of  carbon  dioxide  does 
not  necessarily  render  the  fruit  more  susceptible  to  the  browning.  In 
fact,  the  treatment  with  the  gas  appeared  to  inhibit  the  development 
of  browning. 

The  apples  that  were  held  in  the  carbon  dioxide  for  14  days 
developed  a  disagreeable  alcoholic  taste.  Beyond  the  development  of 
this  taste,  however,  they  remained  apparently  normal.  Apples  which 
were  placed  in  the  gas  for  a  short  length  of  time  exhibited  some 
resistance  to  the  browning  but  still  retained  their  normal  flavor. 

Other  apples  were  stored  in  approximately  40  per  cent  carbon 
dioxide  in  sealed  containers  for  8  weeks.  No  browning  developed  in 
this  fruit  while  it  remained  sealed  in  the  cans,  but  upon  being  exposed 
to  the  air  it  browned  throughout.  This  indicates  that  even  at  this 
per  cent,  when  inclosed,  the  carbon  dioxide  markedly  affected  or 
injured  the  tissues;  hence,  as  soon  as  the  apples  came  in  contact  with 
air  the  cells  browned  through  the  process  of  oxidation. 


BULLETIN  370]       BROWNING    OF    YELLOW    NEWTOWN    APPLES 


23 


Oxygen. — As  the  apple  carries  on  metabolic  activities  while  stored, 
the  question  arises  as  to  whether  its  behavior  with  regard  to  internal 
browning  may  not  be  affected  by  the  restricted  oxygen  supply  in 
storage.  To  test  the  effect  of  an  increased  oxygen  supply,  some  apples 
were  stored  in  sealed  containers  of  normal  air,  while  others  were 
placed  in  containers  in  which  the  oxygen  content  was  kept  above  that 
of  normal  air.    The  results  of  these  tests  are  given  in  table  15. 

TABLE  15 

The  Effect  of  an  Increased  Oxygen  Supply  Upon  the  Development 

of  Internal  Browning 


Degree  of  browning 

Treatment  and  time  stored* 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

normal 

trace 

slight 

mode-ate 

severe 

1. 

Check — in     normal     air — stored     6 

weeks 

0 

20 

35 

38 

8 

2. 

In  40  per  cent  oxygen  stored  6  weeks... . 

0 

29 

26 

45 

0 

3. 

Check — in     normal     air — stored     8 

weeks 

40 

30 

20 

10 

0 

4. 

In  40  per  cent  oxygen  stored  8  weeks 

40 

50 

10 

0 

0 

5. 

In  40  per  cent  oxygen  stored  8  weeks 

30 

35 

25 

10 

0 

6. 

In  70  per  cent  oxygen  stored  8  weeks 

0 

20 

25 

35 

20 

*  Apples  sealed  in  cans. — The  apples  used  in  tests  1  and  2  were  from  different  lots  thanthose  used 
in  tests  3,  4,  5  and  6. 

These  figures  show  that  an  increase  in  the  amount  of  oxygen  above 
that  of  normal  air  has  little  or  no  effect  upon  the  development  of 
browning.  In  the  last  test  where  the  amount  of  oxygen  was  very  high, 
the  fruit  ripened  rapidly  and  the  skin  showed  signs  of  serious  injury. 
Not  even  in  the  cases  where  the  tissues  themselves  escaped  injury  was 
the  difference  in  the  amount  of  browning  sufficient  to  be  indicative  of 
any  control  of  the  disease  by  an  increased  oxygen  supply.  These 
results  are  in  decided  contrast  to  the  uniformly  beneficial  effects  of 
air  circulation  which  are  reported  in  a  later  section  of  this  paper. 


The  Relation  of  Essential  Oils  to  Internal  Browning 

Dixon  and  Atkins7  have  shown  that  anaesthetics  increase  the  per- 
meability of  the  plasma  membrane,  for  the  cell  sap  is  readily  expressed 
after  their  application.  When  applied  for  this  purpose,  however,  the 
anaesthetics  were  toxic  and  their  effect  irreversible.     Osterhout12  in 


24  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

his  work  with  anaesthetics  made  measurements  upon  tissue  to  deter- 
mine whether  the  increase  in  permeability,  usually  observed  to  follow 
their  application,  is  due  to  the  anaesthetics  or  to  toxins.  He  concludes 
that  the  anaesthetics  produce  a  decrease  in  the  permeability  which  is 
reversible  and  that  the  subsequent  increase  in  permeability  is  due  to 
the  accumulation  of  toxic  substances  as  a  results  of  the  action  of  the 
anaesthetics.  In  1910  Armstrong1  and  his  co-workers  showed  that 
under  the  influence  of  anaesthetics  and  certain  other  substances  which 
they  called  hormones,  reactions  occur  in  the  cells  which  indicate  that 
the  enzymes  and  their  substrati  were  brought  into  contact.  Among 
the  results  of  this  mixing  of  the  enzymes  and  substrati,  as  observed  by 
these  workers,  was  an  oxidation  which  resulted  in  pigmentation.  These 
workers  also  state  that  these  phenomena  are  constantly  taking  place 
in  the  plant,  but  under  normal  conditions  their  products  are  passed 
off  before  they  become  injurious.  Under  abnormal  conditions,  how- 
ever, they  may  accumulate  in  sufficient  amount  to  greatly  hinder  the 
activities  of  the  tissues  and  eventually  to  cause  the  death  of  the  cells. 

Giglioli8' 9  found  that  essential  oils  markedly  influence  the  move- 
ment of  water,  enzymes  and  soluble  substance  through  the  cell  mem- 
brane, owing  to  the  rapid  change  in  the  permeability  in  the  plasma 
membrane.  Eecently  Pantanelli13  has  shown  that  the  cells  of  the  endo- 
carp  of  the  mandarin  orange  (Citrus  nobilis),  when  subjected  to  tem- 
peratures very  near  to  freezing,  suffer  a  progressive  increase  in  the 
cell  permeability.  The  increase  in  permeability  was  favored  by  sub- 
stances that  penetrate  rapidly  into  the  cells. 

In  1920,  Power  and  Chestnut16  isolated  the  essential  oils  of  the  apple. 
They  demonstrated  conclusively  that  essential  oils  are  being  produced 
continuously  by  the  apple  in  sufficient  quantities  to  be  detected. 
Brooks,  Cooiey  and  Fisher4' 5- 6  found  that  apple  scald,  a  non-parasitic 
storage  disease  which  is  generally  confined  to  the  surface  of  the  fruit, 
was  apparently  due  to  volatile  substances  which  are  produced  by  the 
fruit  when  held  for  sometime  under  the  more  or  less  abnormal  condi- 
tion of  storage.  As  proof  of  this  contention,  they  present  data  which 
show  that  the  disease  is  reduced  by  removing  these  volatile  substances 
from  the  fruit  by  air  circulation  or  by  storing  the  fruit  in  wax  or  oil 
wrappers  that  are  good  absorbents  of  essential  oils. 

After  making  a  considerable  number  of  observations  upon  the 
appearance  of  the  advanced  stages  of  apple  scald  and  upon  internal 
browning,  the  condition  of  the  tissue  and  the  way  in  which  these 
diseases  spread  into  the  flesh  of  the  fruit,  it  became  apparent  that  there 
was  a  similarity  between  these  two  storage  troubles.  Histological 
examinations  of  affected  tissues  further  emphasized  the  analogy  which 


BULLETIN  370]      BROWNING    OF   YELLOW   NEWTOWN   APPLES 


25 


existed  between  these  diseases.  There  was  no  regularity  about  the 
spread  of  the  disease  from  one  cell  to  the  other  in  the  tissue,  since 
isolated  cells  showing  browning  were  always  found  to  be  scattered 
among  the  normal  cells  near  the  region  of  scald  or  browning.  In  the 
cells  in  which  the  progress  of  the  browning  could  be  followed,  it  was 
found  to  be  identical  in  the  two  diseases,  the  browning  starting  at  the 
periphery  of  the  cell  in  the  vicinity  of  the  nucleus,  and  from  there 
spreading  to  all  parts  of  the  cell.  Plasmolysis  accompanied  the 
advance  in  browning,  until  in  the  severe  stages  the  protoplast  occupied 
only  a  small  fraction  of  the  cell  cavity.  The  cell  wall  remained 
unchanged.  In  order  to  further  test  this  apparent  similarity  between 
the  two  diseases,  experiments  with  treatments  which  had  proved  suc- 
cessful in  reducing  the  amount  of  apple  scald,  were  conducted  to  deter- 
mine their  effectiveness  in  the  control  of  internal  browning. 

Am  Movement  as  a  Preventive  of  Internal  Browning 

During  the  seasons  of  1919-20  and  1920-21  apples  stored  at  32°  F. 
were  placed  in  slat  boxes  and  subjected  to  forced  air  circulation  before 
an  electric  fan  for  10  to  20  minutes  twice  each  week.  One-half  of 
these  apples  were  wrapped  in  commercial  wrappers  while  the  other 
half  were  packed  without  wrapping.  As  a  check,  apples  of  the  same 
lots  in  common  storage  were  used.  In  addition  to  these  tests  apples 
were  also  sealed  in  tin  cans  provided  with  inlet  and  outlet  openings, 
and  subjected  to  a  slow  continuous  air  circulation  maintained  by  an 
aspirator.  Apples  with  and  without  wrappers  were  again  employed 
in  these  tests.    A  summary  of  the  results  is  given  in  table  16. 

TABLE  16 

The  Effect  of  Air  Movement  on  the  Development  of  Internal  Browning 


Condition  of  storage 


Number 
of  tests 


Temper- 
ature of 
storage 


Degree  of  browning 


Per  cent 
normal 


Per  cent 
trace 


Per  cent 
slight 


Per  cent 
moderate 


Per  cent 


Apples  in  common  stor- 
age  

Apples  ventilated  by 
air  circulation,  wrap- 
ped  

Apples  ventilated  by 
air  circulation,  not 
wrapped 


32°F. 


32°F. 


32°F. 


24 


54 


63 


42 


14 


10 


26 


UNIVERSITY    OF    CALIFORNIA— EXPERIMENT    STATION 


The  effect  of  air  circulation  on  the  development  of  the  browning 
is  striking.  The  figures  also  show  a  relation  between  the  effectiveness 
of  the  ventilation  and  the  severity  of  browning  for,  in  every  case  the 
wrapped  fruit  exhibited  more  browning  than  that  not  wrapped.  This 
reduction  by  ventilation  in  the  amount  of  browning  indicates  that  the 
trouble  is  favored  by  the  accumulation  of  deleterious  substances  which 
are  removed  by  air  movement. 

Gas  Absorbents  as  Agencies  in  the  Prevention  of  Internal 

Browning 

On  January  5,  1920,  sixty  specimens  each  of  representative  por- 
tions of  the  fifteen  lots  harvested  during  the  first  and  second  pickings 
of  the  1919  season  were  wrapped  with  oiled  wrappers.  Apples  of  the 
same  lots  in  common  storage  were  used  as  checks.  At  the  time  of  the 
first  two  pickings  for  the  1920  season  eighty  specimens  each  of  two 
lots  were  again  stored  in  wrappers  impregnated  with  different  oils. 
A  summary  of  the  oils  used  and  the  results  obtained  with  these  treat- 
ments at  32°  F.  is  given  in  table  17. 

TABLE  17 

The  Effect  of  Gas  Absorbents  on  the  Development  of  Internal  Browning 


Treatment 


Number 
of  tests 


Number 

of  apples 

used 


Degree  of  browning  after  2J^  months  storage 


Per  cent 
normal 


Per  cent 
trace 


Per  cent 
slight 


Per  cent 
moderate 


Per  cent 


Olive  oil  wrapper 

Cocoa  butter  wrapper 

Vaseline  wrapper 

Paraffin  wrapper 

Common  wrapper 

(ch-ck) 


460 
460 
460 
240 
460 


35 

34 
48 
10 
11 


50 
46 
52 

77 
62 


12 

is 

0 

13 

13 


These  data  indicate  that  the  amount  of  browning  can  be  reduced 
by  employing  substances  which  absorb  essential  oils  or  emanating 
gases.  Since  all  the  tests  as  well  as  the  checks  were  stored  in  identical 
boxes  and  under  as  nearly  as  possible  the  same  conditions  in  the 
storage  room,  the  beneficial  effect  of  the  oil  wrappers  must  lie  in  their 
ability  to  prevent  the  accumulation  of  injurious  substances. 

This  beneficial  effect  of  gas  absorbents  in  the  control  of  browning 
is  shown  even  to  better  advantage  by  tests  with  impregnated  wrappers 
and  other  gas  absorbents  which  were  conducted  in  sealed  containers. 
This  was  thought  to  be  a  more  accurate  method  of  determining  the 


Bulletin  370]     BROWNING  OF  YELLOW 


NEWTOWN    APPLES 


27 


effectiveness  of  these  absorbents  in  the  control  of  the  disease,  since  it 
seemed  logical  to  assume  that  there  is  always  a  considerable  amount 
of  these  esters  or  deleterious  materials  in  the  storage  room  which  the 
wrappers  in  the  open  boxes  would  absorb  as  readily  as  the  substances 
from  the  individual  specimens  that  are  wrapped  and  which  would  soon 
exhaust  their  power  to  function  as  active  absorbents.  In  the  sealed 
containers,  however,  the  absorption  of  substances  would  be  more  nearly 
confined  to  those  given  off  by  the  enclosed  fruit,  which  should  materi- 
ally increase  the  period  of  active  absorption  by  the  oils.  For  these 
experiments  33  specimens  each  of  the  same  lot  picked  October  18,  1920, 
were  used  in  each  test.    The  results  are  given  in  table  18. 


TABLE  18 
The  Effect  of  Gas  Absorbents  on  the  Development  of  Internal  Browning 


Treatment* 


Degree  of  browning  after  11  weeks 


Per  cent 
normal 


Per  cent 
trace 


Per  cent 
slight 


Per  cent 
moderate 


Per  cent 
severe 


Commercial  wrappers 

Cocoa  butter  wrappers 

Olive  oil  wrappers 

Vaseline  wrappers 

Paraffin  wrappers 

Animal  charcoal 

Silica  powder 

225    cc.    cone,    potassium   hydroxide   in 

bottom  of  can 

225  gr.  soda  lime  in  bottom  of  can 


0 
65 
53 
65 
25 
45 

3 

80 
0 


6 
35 
47 
35 
63 
52 

3 

20 
5 


0 
0 
0 
0 
12 
3 
3 

0 
5 


59 
0 
0 
0 
0 
0 

44 

0 
50 


35 
0 
0 
0 
0 
0 

47 

0 
40 


*  All  cans  sealed  with  arrangement  for  slow  renewal  of  air. 

The  data  in  table  18  show  a  striking  correlation  between  the 
prevention  of  browning  and  the  gas  absorbents.  In  these  tests  96 
per  cent  of  the  treated  fruit  was  marketable,  as  compared  with  only  5 
per  cent  of  that  of  the  controls.  The  figures  also  indicate  a  definite 
relation  between  the  capacity  of  the  various  absorbents  for  taking  up 
esters  and  the  prevention  of  the  disease.  Paraffin  which,  according 
to  Gildemeister  and  Hoffman10  has  an  absorbing  power  of  approxi- 
mately one-half  that  of  the  other  substances,  showed  the  least  preven- 
tion of  browning. 

Work  during  the  season  of  1922  indicated  that  oiled  wrappers  were 
more  effective  in  reducing  browning  early  in  the  season.  Late  in  the 
season  the  absorbent  power  of  the  wrappers  was  lost  and  thereafter  the 
oil-wrapped  specimens  browned  more  severely  than  fruit  surrounded 


28  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

by  common  wrappers  not  impregnated  with  oil.  This  is  logical,  since 
the  oiled  wrappers  more  completely  sealed  each  fruit  than  did  the 
common  wrapper.  Furthermore,  where  certain  oils  of  mineral  origin 
were  used  the  absorbent  capacity  more  closely  resembled  that  of 
paraffin  and  the  effect  was  not  so  satisfactory  as  that  obtained  with  the 
vegetable  oils. 

All  the  tests  with  gas  absorbents,  as  well  as  those  with  air  circula- 
tion indicate  that  this  disease  is  caused  by  substances  in  the  nature  of 
essential  oils  or  other  volatile  substances,  which  when  permitted  to 
accumulate,  result  in  the  browning.  This  fact  would  seem  to  place 
internal  browning  and  apple  scald  on  a  similar  basis  with  regard  to 
causative  agent. 

A  question  which  then  arises  is  that  of  the  appearance  of  scald  on 
the  surface,  while  internal  browning  develops  in  the  flesh  of  the  fruit. 
To  answer  this  question  apples  were  placed  in  sealed  containers  at  a 
temperature  and  oxygen  supply  favoring  the  development  of  the 
diseases.  In  most  cases  it  was  found  that  scald  and  browning  developed 
at  a  similar  rate.  The  scald  soon  developed  into  what  is  termed  ' '  deep 
scald, ' '  while  the  browning  rapidly  diffused  outward  from  the  points 
of  initial  appearance  about  the  vascular  bundles.  The  generally 
observed  appearance  of  scald  on  the  surface  without  the  internal 
browning  and  the  reverse  condition  would  then  seem  to  indicate  that 
these  two  regions  of  the  fruit  are  most  susceptible  to  the  action  of 
essential  oils  or  other  deleterious  substances,  or  that  these  substances 
accumulate  more  pronouncedly  in  these  than  in  any  other  regions  of 
the  apple.  The  disease  appears  first  in  that  region  which  is  most 
susceptible.  In  the  Yellow  Newtown  the  region  of  greatest  suscepti- 
bility is  in  the  flesh,  while  in  those  varieties  that  scald  readily,  it  is 
at  the  surface. 

If  internal  browning  and  apple  scald  are  caused  by  the  accumula- 
tion of  essential  oils,  which  can  be  removed  by  ventilation  or  by 
absorption,  the  question  arises  as  to  why  the  preventive  action  of 
ventilation  and  absorbents  is  less  marked  in  the  control  of  internal 
browning  than  in  apple  scald.  This  difference  in  the  effectiveness  of 
the  prevention  is  undoubtedly  due  to  the  fact  that  apple  scald  is  the 
result  of  the  accumulation  of  deleterious  substances  on  the  surfaces 
of  the  fruit  where  the  absorbent  can  be  brought  into  intimate  contact 
with  them.  Internal  browning,  on  the  other  hand,  is  caused  by  an 
accumulation  of  the  deleterious  substances  deep  in  the  tissues  from 
where  they  can  only  be  removed  by  reducing  their  concentration  at 
the  surface,  thereby  inducing  them  to  diffuse  outward,  which  is  a  slow 
process. 


BULLETIN  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  29 


The  Increase  in  Permeability  Prior  to  and  Accompanying  the 
Development  of  Internal  Browning 

If  internal  browning  is  due  to  the  action  of  some  deleterious  sub- 
stance which  tends  to  accumulate  in  the  flesh  of  the  apple  under 
storage  conditions,  there  must  be  some  evidence  of  its  action  before  the 
browning  occurs,  that  is,  certain  alterations  must  occur  in  the  cells 
which  permit  the  browning  to  take  place.  Possibly  the  most  important, 
as  well  as  the  most  probable  change  which  could  take  place  is  that  of 
altering  the  permeability. 

To  determine  any  change  in  the  permeability  which  might  precede 
or  accompany  the  browning,  measurements  were  made  of  the  resist- 
ance offered  to  the  passage  of  an  electric  current.*  These  measure- 
ments indicated  a  great  reduction  in  the  relative  resistance  offered  by 
the  tissue  in  the  region  of  browning  prior  to  the  development  of  any 
noticeable  discoloration.  It  was  also  found  that  the  resistance  con- 
tinued to  decrease  with  the  detectable  appearance  of  the  disease.  For 
example,  in  two  representative  lots  of  apples  held  at  41°  F.,  where 
browning  did  not  develop,  the  relative  resistance  was  2400  ohms ;  while 
in  the  same  lots  at  32°  F.,  where  browning  did  develop  but  before  any 
discoloration  became  noticeable,  the  resistance  was  only  1100  ohms; 
and  in  apples  of  the  same  lots  at  32°  F.  which  showed  trace  browning, 
the  resistance  was  reduced  to  700  ohms.f  The  measurements  also 
showed  that  there  was  no  reduction  in  the  relative  resistance  in  fruit 
stored  at  32°  F.  which  was  resistant  to  the  browning. 

Should  this  apparent  decrease  in  the  resistance  be  due  to  the  action 
of  essential  oils  or  similar  deleterious  substance,  the  resistance  of 
normal  tissue  should  also  decrease  when  treated  with  these  oils.  To 
test  this  property  of  these  substances,  several  essential  oils  as,  Amyl 
Acetate,  Amyl  Valeriate,  Acetaldehyde,  and  others,  in  attenuated 
dilution  (.001  per  cent)  were  applied  to  the  fruit  about  the  electrodes 
of  the  conductivity  apparatus.  After  the  current  had  been  on  con- 
tinuously for  twenty  minutes,  the  resistance  of  the  specimens  treated 
with  water  and  the  untreated  checks  dropped  from  2800  to  2100  ohms, 
while  that  of  the  specimens  treated  with  essential  oils  dropped  from 
2800  to  500  ohms.f  The  measurements  show  conclusively  that  essen- 
tial oils  decrease  the  resistance  to  the  passage  of  an  electric  current 
when  brought  in  contact  with  the  fruit  tissue.     The  decrease  in  the 

*  The  lowering  of  the  resistance  offered  to  the  passage  of  an  electric  current 
indicated  a  relative  increase  in  the  permeability  of  the  cells, 
t  For  additional  data  see  Winkler.19 


30  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

resistance  of  the  untreated  specimens  and.  those  treated  with  water 
was,  no  doubt,  due  to  injury  resulting  from  the  continuous  flow  of  the 
electric  current.  The  data  further  indicate  that  very  minute  accumu- 
lations of  the  essential  oils  might  be  sufficient  to  influence  the  per- 
meability of  the  apple  cell  to  permit  the  oxidase  and  tannins  to  come 
in  contact,  thus  resulting  in  the  browning.  This  is  especially  true 
when  the  attenuated  dilutions  of  the  substances  used  in  these  tests  are 
compared  with  the  normal  essential  oil  content  of  some  apples  as  given 
by  Power  and  Chestnut.10  These  workers  have  shown  that  the  parings 
of  the  Ben  Davis,  an  apple  lacking  in  aroma  as  well  as  flavor,  contain 
essential  oils  in  sufficient  amount  to  equal  about  .0007  per  cent  of  the 
entire  fruit,  while  an  odorous  crab  apple  contained  .0013  per  cent  of 
essential  oils. 

GENERAL  DISCUSSION 

The  fruit  from  trees  that  were  vegetatively  weak  and  also  from 
extremely  vigorous  trees  browned  more  readily  than  fruit  from  trees 
of  normal  vegetative  vigor.  The  age  of  the  tree  exerted  less  influence 
upon  the  browning  than  the  vigor.  This  was  brought  out  by  the  fact 
that  in  1918  and  1919,  just  after  the  young  trees  began  to  produce 
and  when  they  were  much  more  vigorous,  than  the  old  trees,  the  fruit 
of  the  young  trees  browned  the  more  severely.  In  1920,  however, 
when  the  young  trees  had  a  fair  crop  of  fruit  as  compared  with  the 
very  sparse  set  on  the  old  trees  which  at  this  time  also  showed  the 
greatest  vegetative  vigor,  the  percentage  of  browning  was  greater  in 
the  fruit  of  the  old  trees. 

The  investigations  indicate  a  direct  relation  of  temperature  to 
internal  browning.  Lower  temperatures  were  found  to  favor  and 
higher  temperatures  to  oppose  browning,  both  in  the  orchard  and  in 
storage.  The  relationship  of  orchard  temperature  to  browning  was 
most  strikingly  indicated  in  the  case  of  the  fruit  in  black  bags  and 
the  fruit  of  the  tented  or  shaded  tree.  In  the  former  case  the  mean 
daily  temperature,  within  the  fruit  was  about  9°  F.  above  the  tem- 
perature of  the  fruit  normally  exposed,  due  to  heat  absorbed  and 
retained  within  the  black  bags ;  while  the  fruit  on  the  tree  under  the 
unheated  tent,  had  a  mean  daily  temperature  of  about  9°  F.  below  that 
of  fruit  normally  exposed,  owing  to  the  partial  exclusion  of  sunlight. 
After  five  months  storage,  the  average  for  the  seasons  of  1920-21  and 
1921-22  of  the  black-bagged  fruit  was  84  per  cent  normal  as  compared 
with  only  12  per  cent  normal  fruit  from  the  unheated  tented  tree. 
The  normally  exposed  fruit  browned  three  times  as  badly  as  the  black- 


Bulletin  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  31 

bagged  fruit,  but  much  less  than  the  fruit  from  the  tented  tree.  These 
results  point  to  the  possibility  that  the  mean  temperature  for  the  grow- 
ing season  in  the  Pajaro  Valley  hovers  around  the  lower  limit  for  the 
normal  development  of  this  variety  of  apple. 

The  results  obtained  with  the  fruit  from  different  exposures  upon 
the  tree  also  indicate  that  orchard  temperature  greatly  influences  the 
resistance  or  susceptibility  of  the  fruit  to  browning.  Apples  on  the 
same  tree,  well  exposed  with  regard  to  sunlight,  browned  nearly  50 
per  cent  less  than  apples  poorly  exposed.  The  relation  of  defoliation 
and  density  of  foliage  to  the  development  of  browning  as  reported  by 
Ballard  and  others2  gives  additional  evidence  in  attributing  the  sus- 
ceptibility to  browning  of  the  apples  of  this  valley  to  the  low  tempera- 
ture during  the  growing  months.  These  workers  state  that  apples  from 
partially  defoliated  branches  browned  less  than  fruit  from  the  same 
trees  on  branches  carrying  all  their  foliage.  They  also  found  that 
fruit  from  trees  of  unusually  heavy  foliage  browned  more  severely 
than  that  from  trees  with  only  a  moderate  amount  of  foliage.  Their 
figures  on  the  analyses  of  this  fruit  indicate  that  neither  defoliation 
nor  the  different  amounts  of  foliage  influence  the  nutrition  of  the 
fruit  with  respect  to  sugar  or  acid  content  sufficiently  to  account  for 
its  different  behavior  with  regard  to  the  browning  when  placed  in 
storage.  Even  though  Ballard  and  others2  give  no  indication  as  to 
why  the  defoliation  and  the  moderate  foliage  as  compared  with  heavy 
foliage  proved  beneficial  in  reducing  the  browning,  the  writers  believe 
that  these  conditions  of  foliage  permitted  more  direct  sunlight  to  fall 
on  the  fruit  thereby  increasing  the  temperature.  This  indication  is 
substantiated  by  the  fact  that  in  1908  and  1914,  when  the  mean  tem- 
perature for  the  growing  months  was  a  few  degrees  below  the  average 
mean  temperature  for  these  months  for  the  last  seventeen  years,  the 
browning  was  very  severe.  On  the  other  hand,  in  1912,  1913,  1917, 
and  1918,  when  the  mean  temperature  was  several  degrees  above  the 
average  mean  temperature  for  the  growing  months,  there  was  very 
little  or  no  browning.  This  marked  effect  of  the  temperature  upon 
the  browning  was  brought  out  more  strikingly  in  storage.  For 
example,  at  30°,  32°,  36°,  40°,  and  45°  F.  the  percentage  of  normal 
fruit  after  four  months  storage  was  10,  15,  35,  74  and  95  per  cent, 
respectively. 

In  view  of  the  above  correlation  of  the  browning  with  lower  mean 
temperatures  it  also  seems  possible  that  the  more  severe  browning  of 
the  mature  fruit  was  due  to  its  being  exposed  to  the  lower  temperature 
which  prevailed  during  the  latter  part  of  the  harvesting  season.  The 
fruit  of  the  second  picking  was  exposed  for  three  weeks  after  the  fruit 


32  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

of  the  first  picking  was  harvested  to  a  mean  temperature  of  about  4° 
to  5°  F.  below  the  mean  temperature  of  the  growing-  season.  The 
fruit  picked  November  6  and  November  22  was  exposed  for  six  to 
eight  weeks  to  the  influence  of  a  mean  daily  temperature  of  4°  to  14°  F. 
below  that  prevailing  at  the  time  and  before  the  first  picking  was 
made.  The  fruit  of  the  1922  season,  which  was  harvested  fully  a 
month  later  than  the  normal  harvest  season,  browned  more  severely 
in  storage  than  either  of  the  two  preceding  crops.  These  data  point 
to  the  possibility  that  the  low  temperature  favors  those  conditions 
within  the  fruit  which  are  necessary  for  the  development  of  browning. 
This  weakness  in  the  fruit,  however,  if  it  can  be  considered  as  such, 
may  be  due  to  an  abnormal  development  of  the  protoplasmic  structure 
of  the  apples  or  to  an  accumulation  of  some  deleterious  substance  which 
brings  about  a  more  rapid  cessation  in  the  normal  functioning  of  these 
structures  in  storage.  This  seems  probable  since  there  was  no  appre- 
ciable difference  between  the  fruit  resistant  and  that  susceptible  to 
browning  in  those  constituents  such  as  sugars  and  acid  and  the  pH 
value  of  the  expressed  juice,  which  might  be  expected  to  influence  a 
reaction  of  this  sort. 

The  accumulation  of  essential  oils  or  similar  deleterious  substances 
also  seems  to  be  linked  with  the  weakness  which  shows  up  in  these 
apples  in  storage.  This  is  indicated  by  the  great  reduction  in  the 
amount  of  browning  that  is  brought  about  through  the  employment  of 
air  circulation  or  the  impregnation  of  the  wrappers  with  good  absorb- 
ents for  these  substances.  It  has  been  further  demonstrated  that  the 
permeability  of  the  cells,  which  is  the  most  probable  change  that  might 
precede  this  browning  or  similar  reactions,  is  increased  rapidly  by 
essential  oils  when  applied  even  in  great  dilution  to  the  apple  tissue. 
It  was  also  found  that  there  was  an  increase  in  permeability  prior  to 
the  death  of  the  cells  in  the  apple  regardless  of  whether  death  was  due 
to  the  usual  type  of  storage  breakdown  that  is  the  result  of  over- 
ripening,  or  to  internal  browning. 

The  data  obtained  upon  the  relationship  of  temperature  and  the 
accumulation  of  essential  oils  or  similar  volatile  substances  to  the 
browning,  although  not  conclusive,  point  to  several  possibilities  con- 
cerning the  cause  of  this  disease.  When  these  apples  are  grown  at  a 
mean  temperature  as  low  as  that  of  the  growing  season  of  the  Pajaro 
Valley,  they  fail  to  develop  normally,  hence  when  they  are  placed  in 
storage  the  flesh  of  the  fruit  exhibits  a  susceptibility  to  injury  through 
the  action  of  the  volatile  emanation  of  the  apple.  This  is  indicated  by 
the  behavior  of  the  fruit  from  different  regions  as  well  as  by  that  from 
under  the  tent  and  from  the  black  bags.    The  lower  temperature  may 


BULLETIN  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  33 

not  only  affect  the  development  of  the  fruit,  but  it  also  seems  to  influ- 
ence the  production  or  accumulation  of  the  volatile  substances  which 
are  immediately  responsible  for  the  browning-.  This  becomes  apparent 
when  the  great  difference  in  the  amount  of  browning  which  developed 
at  the  several  storage  temperatures  is  taken  into  account.  At  the  lower 
temperatures  there  must  be  a  greater  production  of  these  substances 
or  else  they  must  accumulate  more  rapidly  in  those  regions  of  the 
torus  that  are  first  to  show  the  browning.  The  reduction  in  the 
development  of  the  browning  by  the  use  of  gas  absorbents  also  indi- 
cates that  these  volatile  substances  are  present  in  injurious  amounts  at 
the  lower  temperatures  under  the  ordinary  conditions  of  storage.  The 
more  rapid  accumulation  of  the  deleterious  substances  may  seem  the 
more  probable  way  of  accounting  for  the  injurious  amount  of  these 
substances  when  the  decrease  in  their  volatility  and  the  decrease  in  the 
permeability  of  the  tissue  at  the  lower  temperatures  is  considered.  It 
is,  however,  not  at  all  unlikely  that  there  is  also  a  greater  production 
of  these  substances  under  the  somewhat  abnormal  conditions  of  the 
lower  temperatures  of  storage. 

The  nature  of  the  process  which  results  in  the  browning  becomes 
of  interest  in  connection  with  the  above  possibilities  as  to  the  cause  of 
this  trouble.  A  plausible  explanation  of  this  process  would  be  to 
attribute  it  to  an  increase  in  the  permeability  of  the  protoplasm  which 
permits  the  enzymes  and  their  substrati  to  mix.  These  changes  might 
be  brought  about  by  the  accumulation  of  certain  substances  as  the 
essential  oils  which  are  produced  by  the  apple  in  storage,  and  which 
apparently  have  a  toxic  effect  upon  the  protoplasm  of  the  cells.  In  the 
normal  cells,  the  enzymes  are  prevented  from  acting  upon  their  sub- 
strati  through  lack  of  contact  due  to  the  possible  impermeable  nature 
of  the  phase  surfaces  of  the  protoplasm  to  these  substances.  When  the 
phase  arrangements  in  the  protoplasm,  however,  are  acted  upon  by 
toxins,  these  substances  are  no  longer  prevented  from  coming  into 
contact.  As  a  result  of  this  liberation,  the  tannins  of  the  apple  cells 
may  be  oxidized  to  a  brown  by  the  oxidase  present  in  the  mature  fruit. 
It  has  been  indicated  by  Bartholomew3  that  similar  changes  precede 
the  blackening  of  the  tissue  in  "Blackheart"  of  potatoes.  This 
explanation  of  the  coloration  as  based  upon  a  change  in  the  per- 
meability is  also  supported  by  the  fact  that  before  browning  occurs 
there  is  a  great  increase  in  the  permeability  of  the  cells  as  indicated 
by  the  conductivity  measurements. 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


SUGGESTIONS  FOR  THE  CONTROL  OF  INTERNAL 
BROWNING 

Since  the  temperature  that  prevails  in  the  Pajaro  Valley  during 
the  growing  months  and  which  cannot  be  controlled,  seems  to  be  the 
potent  factor  in  rendering  the  Yellow  Newtown  susceptible  to  brown- 
ing, it  becomes  necessary  to  control  the  development  of  this  trouble 
after  the  fruit  reaches  maturity.  Should  this  be  true,  there  are  two 
ways  open  for  a  solution  of  the  problem.  The  first,  which  would  aim 
at  a  direct  control,  consists  of  the  employment  of  those  practices  which 
prevent  the  further  development  of  the  disease  in  storage.  A  second 
solution,  which  is  indirect,  would  consist  in  supplanting  the  Yellow 
Newtown  with  a  variety  that  is  not  so  seriously  affected  by  the  low 
temperature  of  the  growing  months  of  the  Pajaro  Valley. 

Early  Harvesting  as  a  Means  of  Controlling  Internal  Browning. — 
Apparently  the  first  step  in  the  control  of  this  trouble  after  the  fruit 
reaches  maturity  is  that  of  harvesting  the  crop  as  early  as  possible. 
The  low  mean  temperature  seems  to  be  involved  in  rendering  these 
apples  susceptible  to  browning.  Hence,  the  fruit  which  is  permitted 
to  remain  on  the  trees  until  late  in  the  season,  when  the  mean  tem- 
perature is  much  below  that  of  the  growing  months,  might  be  expected 
to  brown  more  readily.  The  records  of  several  seasons  during  which 
tests  have  been  in  progress,  indicate  that  this  is  what  happens.  For 
example,  each  of  the  pickings  of  September  27,  October  16,  and  Novem- 
ber 6,  1920,  showed  approximately  60  per  cent  of  marketable  fruit 
after  20,  15  and  6  weeks  storage,  respectively.  These  figures  represent 
the  results  obtained  from  fruits  of  the  same  trees  stored  at  32°  F. 
In  fact,  all  the  data  collected  in  connection  with  the  different  dates  of 
harvesting  indicate  that  it  would  be  a  desirable  practice  for  the 
growers  to  harvest  their  fruit  as  soon  as  possible  after  it  is  sufficiently 
ripe  for  picking. 

Storing  Apples  at  37°  to  40°  F.  to  Control  the  Browning. — The 
most  promising  method  for  the  control  of  browning,  after  the  fruit  is 
harvested,  is  that  of  prompt  storage  at  temperatures  of  37°  to  40c  F. 
The  practice  of  delayed  storage  or  even  a  delay  in  getting  the  fruit 
into  storage  has  in  all  tests  increased  the  subsequent  amount  of  brown- 
ing. With  prompt  storage  at  the  above  mentioned  temperatures  the 
percentage  of  browning  on  April  1,  after  six  months  storage,  was  less 
than  15  per  cent  and  the  browning  that  did  occur  was  of  a  mild  nature 
which  would  not  interfere  with  the  commercial  value  of  the  fruit. 


Bulletin  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  35 

Fruit  from  the  same  trees  stored  at  32°  F.  showed  100  per  cent  of 
browning  before  this  time,  60  per  cent  of  this  fruit  being  so  severely 
browned  as  to  render  it  unmarketable.  In  this  connection,  however, 
the  question  arises  as  to  whether  the  loss  through  rot  at  these  tem- 
peratures might  not  be  sufficient  to  off-set  the  benefit  derived  from  the 
avoidance  of  browning.  This  would,  no  doubt,  be  the  result  with  many 
varieties  of  apples  if  they  were  stored  at  37°  to  40°  F.  The  Yellow 
Newtown,  however,  is  one  of  the  best  keepers,  and  when  stored  at  these 
temperatures  during  the  past  two  years  there  was  practically  no  rot, 
even  though  the  fruit  was  tree-run  and  had  not  been  sorted. 

Ventilation  in  Storage  as  a  Means  of  Controlling  the  Browning. — 
A  second  method  whereby  the  development  of  the  browning  may  be 
controlled  in  storage  is  that  of  ventilation.  This  method  may  be  of 
value  where  the  storage  facilities  are  such  that  it  becomes  necessary  to 
store  these  apples  below  36°  F.  The  unwrapped  fruit,  stored  at  32°  F. 
and  ventilated  before  a  fan  for  10  to  20  minutes  twice  each  week 
showed  only  14  per  cent  of  mild  browning  on  April  1,  compared  with 
76  per  cent  of  browning  for  the  fruit  in  ordinary  commercial  storage, 
13  per  cent  of  the  browning  in  the  latter  case  being  of  such  severity 
as  to  render  the  fruit  unfit  for  consumption.  Further  experiments 
will  be  necessary,  however,  before  definite  recommendations  can  be 
made  for  the  use  of  ventilation  to  prevent  browning. 

Predicting  Browning  Prior  to  Storage. — As  indicated  by  the 
results  of  this  investigation,  the  mean  temperature  of  the  growing 
months  appears  to  be  the  potent  factor  in  rendering  the  Yellow  New- 
town apple  susceptible  to  browning.  If  future  studies  substantiate  this 
apparent  relationship  of  orchard  temperature  to  browning,  it  should 
then  be  possible,  by  consulting  the  Climatological  Data  Reports  of  the 
U.  S.  Weather  Bureau  for  the  growing  months,  to  predict  the  approxi- 
mate amount  of  browning  which  will  occur  during  the  storage  season 
of  these  apples.  In  years  of  possible  severe  browning,  growers  could 
dispose  of  their  crop  early  and  avoid  loss  through  this  disease.  When 
little  or  no  browning  threatens,  the  Yellow  Newtown  could  be  stored 
and  the  profit  secured  from  a  late-keeping  variety  of  the  best  quality 
and  flavor. 

Elimination  of  Browning  Through  More  Resistant  Varieties. — An 
indirect  method  of  overcoming  the  difficulty  of  browning  would  be 
to  supplant  the  Yellow  Newtown  with  some  variety  that  is  not  so 
seriously  affected  by  the  low  temperature  of  the  growing  months  of 
the  Valley.  This  method  of  solving  the  problem,  however,  is  not  as 
readily  carried  out  as  might  appear  on  first  thought.     Mr.  Rodgers, 


36  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

the  father  of  the  Rodgers  brothers  from  whom  the  fruit  for  these  tests 
was  obtained,  undertook  to  find  a  variety  which  could  be  used  to  sup- 
plant the  Yellow  Newtown.  He  introduced  a  great  number  of  apple 
varieties  of  commercial  importance  and  was  finally  forced  to  the  con- 
clusion that  the  Yellow  Newtown  and  the  Yellow  Bellflower  are  the 
only  commonly  known  varieties  that  produce  profitably  under  the 
climatic  conditions  of  the  Pajaro  Valley.  Nevertheless,  it  may  yet 
be  possible  to  find  a  variety  that  will  take  the  place  of  the  Yellow  New- 
town, although  this  will  require  years  of  searching  and  the  testing  of 
a  great  number  of  varieties.  In  view  of  the  present  effort  in  bud 
selection,  it  may  be  possible  to  isolate  a  strain  of  Yellow  Newtown 
which  is  resistant  to  browning.  The  Yellow  Bellflower  might  be 
planted  more  widely  since  it  is  a  fall  apple,  and  as  a  result,  is  con- 
sumed before  losses  due  to  browning  occur.  The  Yellow  Bellflower, 
however,  ranks  below  the  Yellow  Newtown  in  quality,  yield  and 
appearance,  and  cannot  be  expected  to  supplant  the  Yellow  Newtown. 


SUMMARY 

1.  Internal  browning  is  a  non-parasitic  disease  of  the  large  isodia- 
metric  cells  of  the  flesh  of  the  fruit. 

2.  Yellow  Newtown  apples,  regardless  of  where  grown,  have  been 
in  some  years,  susceptible  to  internal  browning.  Nevertheless,  this 
variety  when  grown  under  the  conditions  prevailing  in  the  Pajaro 
Valley,  is  more  susceptible  to  this  disease  than  when  grown  in  other 
fruit  regions. 

3.  The  results  of  the  studies  showed  a  relation  between  tree  age  and 
internal  browning;  fruit  from  old  trees  browned  more  severely  than 
fruit  from  young  trees.  Differences  in  the  maturity  of  fruit  from  old 
and  young  trees  at  harvest  time  probably  affected  the  degree  of 
browning. 

4.  Fruit  from  trees  bearing  a  heavy  crop  was  less  susceptible  to 
browning  in  storage  than  fruit  from  trees  bearing  a  light  crop. 

5.  Fruit  from  trees  of  normal  vegetative  vigor  exhibited  the  most 
resistance  to  browning;  fruit  from  trees  vegetatively  weak  or  froin 
trees  of  extreme  vegetative  vigor  was  more  susceptible  to  browning. 
The  decrease  in  resistance,  however,  was  most  marked  in  the  fruit  from 
the  very  weak  trees. 

6.  The  degree  of  browning  increased  in  severity  with  the  maturity 
of  the  fruit;  that  is,  the  later  the  fruit  was  picked,  the  greater  the 


BULLETIN  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  37 

amount  of  browning  which  occurred  in  storage,  and  the  more  rapidly 
it  developed. 

7.  Chemical  analyses  of  the  fruit  indicated  that  there  was  no  rela- 
tion between  the  sugar  and  acid  content  of  the  apples  and  their 
resistance  or  susceptibility  to  this  disease. 

8.  No  relation  was  found  to  exist  between  the  amount  of  brown- 
ing and  the  pH  value  of  the  expressed  juice  of  the  apples. 

9.  A  lowering  of  the  mean  orchard  temperature  of  about  5°  F. 
during  the  growing  season,  by  tenting  or  shading  a  tree,  greatly 
increased  the  susceptibility  of  the  fruit  to  browning.  After  five 
months  storage  at  32°  F.  the  fruit  of  trees  in  unheated  tents  showed 
50  per  cent  less  normal  specimens  than  that  of  adjacent  trees  which 
were  normally  exposed. 

10.  An  increase  of  10°  F.  in  the  mean  orchard  temperature  by 
bagging  individual  apples  in  black  cloth  during  the  growing  months, 
markedly  increased  the  resistance  of  the  fruit  to  this  disease.  The 
bagged  apples  showed  two-thirds  more  normal  specimens  after  five 
months  storage  at  32°  F.  than  the  normally  exposed  fruit  of  the  same 
trees. 

11.  Fruit  from  the  interior  shaded  portions  of  the  tree  browned 
twice  as  badly  as  fruit  from  the  exposed  portions  of  the  treo  where 
the  temperature  was  14°  F.  higher. 

12.  Some  evidence  was  obtained  to  show  that  self-pollination 
and  cross-pollination  are  factors  which  do  not  materially  affect  the 
development  of  browning. 

13.  Delayed  storage  rendered  the  fruit  more  susceptible  to  brown- 
ing. 

14.  Intermittent  storage  gave  no  promise  as  a  means  of  control  of 
this  disease. 

15.  No  serious  browning  occurred  even  after  five  months  storage 
in  the  fruit  stored  at  45°  F.  or  above. 

16.  The  browning  at  the  end  of  six  months'  storage  at  40°  F.  was 
limited  and  mild,  and  insufficient  to  interfere  with  the  commercial 
value  of  the  fruit. 

17.  At  36°  F.  approximately  65  per  cent  of  the  apples  showed 
browning  by  April  1,  during  each  of  the  seasons  for  which  records 
are  available. 

18.  At  32°  F.  nearly  all  of  the  fruit  showed  browning  by  April  1, 
or  shortly  thereafter,  each  season. 


38  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

19.  It  was  shown  that  the  accumulation  of  carbon  dioxide  in  the 
storage  rooms  does  not  favor  browning.  In  fact,  the  storage  of  the 
fruit  for  several  days  in  pure  carbon  dioxide  increased  its  resistance 
to  the  disease. 

20.  An  increase  in  the  oxygen  supply  did  not  oppose  browning. 

21.  Browning  was  greatly  reduced  by  ventilating  the  fruit.  This 
treatment  was  equally  effective  regardless  of  whether  the  ventilation 
was  rapid  and  intermittent  or  slow  and  continuous. 

22.  The  browning  was  reduced  during  the  early  part  of  the  season 
by  impregnating  the  wrappers  with  oils  and  waxes  which  are  good 
absorbents  of  essential  oils.  Oils  of  low  absorbent  capacity  increased 
the  browning  by  preventing  the  escape  of  the  emanations. 

23.  By  measuring  the  electrical  resistance  of  the  apple  tissue,  it 
was  found  that  there  was  an  increase  in  permeability  prior  to  the  end 
of  the  storage  life  of  the  apple,  regardless  of  whether  death  was  due 
to  the  usual  storage  breakdown  or  to  internal  browning. 

24.  It  was  demonstrated  that  essential  oils  when  applied  to  the 
apple  tissue,  even  in  great  dilution,  rapidly  increase  its  permeability. 

25.  The  data  indicated  that  internal  browning  is  due  to  the  accu- 
mulation of  essential  oils  or  similar  deleterious  substances  which  are 
produced  by  the  apples  in  storage.  This  signified  that  internal  brown- 
ing and  apple  scald  were  quite  closely  related  with  respect  to  cause. 

26.  Hypotheses  have  been  offered  in  explanation  of  the  nature  of 
browning  and  the  greater  susceptibility  of  the  Yellow  Newtown  apple 
to  the  disease  when  grown  under  the  conditions  that  prevail  in  the 
Pajaro  Valley. 

27.  Practical  suggestions  for  the  control  of  internal  browning  have 
been  given. 

ACKNOWLEDGMENTS 

The  writers  wish  to  acknowledge  their  indebtedness  to  Professor 
J.  C.  Whitten  for  suggestions  and  criticisms  given  before  his  untimely 
death,  and  to  Dr.  J.  P.  Bennett  for  counsel  during  the  progress  of  this 
investigation. 

Furthermore,  the  writers  are  indebted  to  Professor  R.  H.  Taylor 
for  preliminary  work  during  the  season  of  1917-18 ;  to  Messrs.  S.  H. 
Cameron  and  J.  L.  Fidler  who  assisted  during  seasons  of  1921-22  and 
1922-23,  respectively ;  and  to  Mr.  L.  P.  Latimer  who  was  responsible 
for  the  temperature  control  during  1921  to  1923,  inclusive. 


BULLETIN  370]      BROWNING   OF   YELLOW   NEWTOWN   APPLES  39 


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